Biliary secretion of alpha-tocopherol and the role of the mdr2 P-glycoprotein in rats and mice.
The mechanism by which alpha-tocopherol (alpha-T) is secreted into the bile is not known; however, we have previously demonstrated that treatment with piperonyl butoxide (PIP, 1 g/kg) results in increased biliary output of both alpha-T and phosphatidylcholine within 3 h of ip injection in rats and that the biliary output of both substances was prevented by chemicals that disrupt microtubules (Toxicol. Appl. Pharmacol. 139, 411-417 (1996)). The P-glycoprotein (Pgp) encoded by the mdr2 gene has been shown to transport phosphatidylcholine into the bile; therefore, in the current study, we utilized the Pgp inhibitor verapamil to investigate the possible involvement of Pgps in the biliary secretion of alpha-T. When rats were iv injected with verapamil (4 mg/kg) 10 min prior to PIP treatment, verapamil prevented the PIP-induced increases in biliary alpha-T and phosphatidylcholine output and resulted in biliary alpha-T outputs that were significantly less than controls. Also, we determined that the biliary alpha-T levels in mdr2 knockout mice were 25% of those in wildtype mice; furthermore, mdr2 liver, lung, and kidney levels of alpha-T and glutathione differed from those of wildtype. To investigate the fate of biliary alpha-T, we injected 14C-labeled alpha-T into the bile duct cannulae of rats and determined that approximately 60% of the radioactivity was reabsorbed within 1 h. Our results indicate that alpha-T undergoes enterohepatic circulation and that the biliary secretion of alpha-T, basally and following chemical treatment, is dependent on the presence of a functioning mdr2 Pgp in rats and mice.
Mustacich
D J
DJ
Department of Biochemistry and Biophysics, Oregon State University, ALS 2011, Corvallis, Oregon 97331-7305, USA.
Shields
J
J
Horton
R A
RA
Brown
M K
MK
Reed
D J
DJ
D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000502:physiology*; D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D000818:Animals; D001646:Bile / Q000737:chemistry*; D001647:Bile Acids and Salts / Q000032:analysis; D002250:Carbon Radioisotopes / Q000378:metabolism; D005260:Female; D005978:Glutathione / Q000032:analysis; D019803:Glutathione Disulfide / Q000032:analysis; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D010713:Phosphatidylcholines / Q000378:metabolism; D010882:Piperonyl Butoxide / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014700:Verapamil / Q000494:pharmacology; D014810:Vitamin E / Q000032:analysis / Q000378:metabolism*
D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D001647:Bile Acids and Salts; D002250:Carbon Radioisotopes; D010713:Phosphatidylcholines; D014810:Vitamin E; C095122:multidrug resistance protein 3; D014700:Verapamil; D005978:Glutathione; D010882:Piperonyl Butoxide; D019803:Glutathione Disulfide